Force imaging input device and system

ABSTRACT

A force imaging touch pad includes first and second sets of conductive traces separated by a spring membrane. When a force is applied, the spring membrane deforms moving the two sets of traces closer together. The resulting change in mutual capacitance is used to generate an image indicative of the amount or intensity of the applied force. A combined location and force imaging touch pad includes two sets of drive traces, one set of sense traces and a spring membrane. In operation, one of the drive traces is used in combination with the set of sense traces to generate an image of where one or more objects touch the touch pad. The second set of drive traces is used in combination with the sense traces and spring membrane to generate an image of the applied force&#39;s strength or intensity.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 11/278,080, entitled “Force Imaging Input Device and System,” filed Mar. 30, 2006, the disclosure of which is herein incorporated by reference in its entirety.

BACKGROUND

The invention relates generally to electronic system input devices and, more particularly, to force imaging and location-and-force imaging mutual capacitance systems.

Numerous touch sensing devices are available for use in computer systems, personal digital assistants, mobile phones, game systems, music systems and the like (i.e., electronic systems). Perhaps the best known are resistive-membrane position sensors which have been used as keyboards and position indicators for a number of years. Other types of touch sensing devices include resistive tablets, surface acoustic wave devices, touch sensors based on resistance, capacitance, strain gages electromagnetic sensors or pressure sensors, and optical sensors. Pressure sensitive position sensors have historically offered little benefit for use as a pointing device (as opposed to a data entry or writing device) because the pressure needed to make them operate inherently creates stiction between the finger and the sensor surface. Such stiction has, in large measure, prevented such devices from becoming popular.

Owing to the growth popularity of portable devices and the attendant need to integrate all input functions into a single form factor, the touch pad is now one of the most popular and widely used types of input device. Operationally, touch pads may be categorized as either “resistive” or “capacitive.” In resistive touch pads, the pad is coated with a thin metallic electrically conductive layer and resistive layer. When the pad is touched, the conductive layers come into contact through the resistive layer causing a change in resistance (typically measured as a change in current) that is used to identify where on the pad the touch event occurred. In capacitive touch pads, a first set of conductive traces run in a first direction and are insulated by a dielectric insulator from a second set of conductive traces running in a second direction (generally orthogonal to the first direction). The grid formed by the overlapping conductive traces create an array of capacitors that can store electrical charge. When an object is brought into proximity or contact with the touch pad, the capacitance of the capacitors at that location change. This change can be used to identify the location of the touch event.

One drawback to using touch pads as input devices is that they do not generally provide pressure or force information. Force information may be used to obtain a more robust indication of how a user is manipulating a device. That is, force information may be used as another input dimension for purposes of providing command and control signals to an associated electronic device. Thus, it would be beneficial to provide a force measurement system as part of a touch pad input device.

SUMMARY

In one embodiment the invention provides a force sensitive touch pad that includes first and second sets of conductive traces separated by a spring membrane. When a force is applied, the spring membrane deforms moving the two sets of traces closer together. The resulting change in mutual capacitance is used to generate an image indicative of the location (relative to the surface of the touch pad) and strength or intensity of an applied force. In another embodiment, the invention provides a combined location and force sensitive touch pad that includes two sets of drive traces, one set of sense traces and a spring membrane. In operation, one of the drive traces is used in combination with the set of sense traces to generate an image of where one or more objects touch the touch pad. The second set of drive traces is used in combination with the sense traces and spring membrane to generate an image of the applied force's strength or intensity and its location relative to the touch pad's surface. Force touch pads and location and force touch pads in accordance with the invention may be incorporated in a variety of electronic devices to facilitate recognition of an increased array of user manipulation.

In yet another embodiment, the described force sensing architectures may be used to implement a display capable of detecting the amount of force a user applies to a display (e.g., a liquid crystal display unit). Display units in accordance with this embodiment of the invention may be used to facilitate recognition of an increased array of user input.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows, in exploded perspective view, a force detector in accordance with one embodiment of the invention.

FIGS. 2A and 2B show, in cross-section, an unloaded (A) and loaded (B) force detector in accordance with FIG. 1.

FIG. 3 shows, in block diagram form, a force detection system in accordance with one embodiment of the invention.

FIG. 4 shows, in block diagram form, a more detailed view of the force detection system in accordance with FIG. 3.

FIG. 5 shows, in cross-section, a location and force detection device in accordance with one embodiment of the invention.

FIG. 6 shows, in cross section, a location and force detection device in accordance with another embodiment of the invention.

FIG. 7 shows an exploded view of drive and sense traces in accordance with FIG. 6.

FIGS. 8A-8C show various views of a location and force detection device in accordance with still another embodiment of the invention.

FIGS. 9A-9C show various views of a location and force detection device in accordance with yet another embodiment of the invention.

FIGS. 10A and 10B show, in cross section, a location and force detection device in accordance with another embodiment of the invention.

FIGS. 11A-11C show various views of a spring membrane in accordance with another embodiment of the invention.

FIGS. 12A and 12B show, in block diagram form, a force detection display system in accordance with one embodiment of the invention.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled in the art to make and use the invention as claimed and is provided in the context of the particular examples discussed below (touch pad input devices for personal computer systems), variations of which will be readily apparent to those skilled in the art. Accordingly, the claims appended hereto are not intended to be limited by the disclosed embodiments, but are to be accorded their widest scope consistent with the principles and features disclosed herein. By way of example only, force imaging systems in accordance with the invention are equally applicable to electronic devices other than personal computer systems such as computer workstations, mobile phones, hand-held digital assistants and digital control panels for various machinery and systems (mechanical, electrical and electronic).

Referring to FIG. 1, the general concept of a force detector in accordance with the invention is illustrated as it may be embodied in touch pad device 100. As illustrated, force detector 100 comprises cosmetic layer 105, sense layer 110 (including conductive paths 115 and electrical connector 120), dielectric spring layer 125 (including spatially offset raised structures 130), drive layer 135 (including conductive paths 140 and electrical connector 145) and base or support 150. (It will be understood by those of ordinary skill in the art that connectors 120 and 145 provide unique connections for each conductive trace on layers 110 and 135 respectively.)

Cosmetic layer 105 acts to protect other elements of the system from ambient conditions (e.g., dust and moisture) and, further, provides a surface through which users interact with detector 100. Conductive paths 115 on sense layer 110 are arranged so that they overlap conductive paths 140 on drive layer 135, thereby forming capacitors whose plates (conductive paths 115 and 140) are separated by sense layer substrate 110, dielectric spring layer 125 and raised structures 130. Dielectric spring layer 125 and raised structures 130 together create a mechanism by which sense layer 110's conductive paths 115 are brought into closer proximity to drive layer 135's conductive paths 140 when a force is applied to cosmetic layer 105. It will be recognized that this change in separation causes the mutual capacitance between sense layer and drive layer conductive paths (115 and 140) to change (increase)—a change indicative of the amount, intensity or strength of the force applied to cosmetic layer 105. Base or support layer 150 provides structural integrity for force detector 100.

Referring to FIG. 2A, a cross-sectional view of force detector 100 is shown in its unloaded or “no force” state. In this state, the mutual capacitance between sense layer 110 and drive layer 135 conductive paths (115 and 140) results in a steady-state or quiescent capacitance signal (as measured via connectors 120 and 145 in FIG. 1). Referring to FIG. 2B, when external force 200 is applied to cosmetic layer 105, dielectric spring layer 125 is deformed so that sense layer 110 moves closer to drive layer 135. This, in turn, results in a change (increase) in the mutual capacitance between the sense and drive layers—a change that is approximately monotonically related to the distance between the two and, therefore, to the intensity or strength of applied force 200. More specifically, during operation traces 140 (on drive layer 135) are electrically stimulated one at a time and the mutual capacitance associated with the stimulated trace and each of traces 115 (on sense layer 110) is measured. In this way an image of the strength or intensity of force 200 applied to cosmetic layer 105 is obtained. As previously noted, this change in mutual capacitance may be determined though appropriate circuitry.

Referring to FIG. 3, a block diagram of force imaging system 300 utilizing force detector touch pad 100 is shown. As illustrated, force imaging system 300 comprises force detector 100 coupled to touch pad controller 305 through connectors 120 (for sense signals 310) and 145 (for drive signals 315). Touch pad controller 305, in turn, periodically sends signals to host processor 320 that represent the (spatial) distribution of force applied to detector 100. Host processor 320 may interpret the force information to perform specified command and control actions (e.g., select an object displayed on display unit 325).

Referring to FIG. 4, during operation drive circuit 400 in touch pad controller 305 sends (“drives”) a current through drive signals 315 and connector 145 to each of the plurality of drive layer conductive paths 140 (see FIG. 1) in turn. Because of capacitive coupling, some of this current is carried through to each of the plurality of sense layer conductive paths 115 (see FIG. 1). Sensing circuits 405 (e.g., charge amplifiers) detect the analog signal from sense signals 310 (via connector 120) and send them to analysis circuit 410. One function of analysis circuit 410 is to convert the detected analog capacitance values to digital form (e.g., through A-to-D converters). Another function of analysis circuit is to queue up a plurality of digitized capacitance values for transmission to host processor 320 (see FIG. 3). Yet another function of analysis circuit is to control drive circuit 400 and, perhaps, to dynamically adjust operation of sense circuits 405 (e.g., such as by changing the threshold value at which a “change” in capacitance is detected). One embodiment of controller 305 suitable for use in the present invention is described in U.S. patent application entitled “Multipoint Touch Screen Controller,” Ser. No. 10/999,999 by Steve Hotelling, Christoph Krah and Brian Huppi, filed 15 Mar. 2006 and which is hereby incorporated in its entirety.

In another embodiment, a force detector in accordance with the invention is combined with a capacitive location detector to create a touch pad device that provides both location and force detection. Referring to FIG. 5, combined location and force detector 500 comprises cosmetic layer 505, circuit board or substrate 510 (including a first plurality of conductive drive paths 515 on a first surface and a plurality of sense paths 520 on a second surface), dielectric spring layer 525 (including alternating, or spatially offset, raised structures 530), drive layer 535 (including a second plurality of conductive drive paths) and base or support 540. In one embodiment, conductive drive paths 515 and 535 are laid down on substrate 510 and support 540 respectively to form rows and sense conductive paths are laid down on substrate 510 to form columns. Accordingly, during operation first drive paths 515 are driven (one at a time) during a first time period and, during this same time, sense paths 520 are interrogated to obtain an image representing the location of one or more cosmetic layer touches. Similarly, second drive paths 535 are driven (one at a time) during a second time period and, during this same time, sense paths 520 are again interrogated to obtain an image representing, this time, the strength or intensity of the force applied to cosmetic layer 505. The operation of computer input devices (e.g., touch pads) for touch detection based on the principle of mutual capacitance is described in U.S. patent application entitled “Multipoint Touchscreen” by Steve Hotelling, Joshua A. Strickon and Brian Q. Huppi, Ser. No. 10/840,862 and which is hereby incorporated in its entirety.

Referring to FIG. 6, location and force touch pad 600 in accordance with another embodiment of the invention is shown in cross section. In this embodiment, cosmetic layer 605 comprises a polyester or polycarbonate film. Layer 610 comprises an acrylic-based pressure sensitive or ultraviolet light cured adhesive. Layer 615 functions as a two-sided circuit board that has a first plurality of conductive drive traces 620 oriented in a first direction on a “top” surface (i.e., toward cosmetic layer 605) and a plurality of conductive sense traces 625 oriented in a second direction on a “bottom” surface. In one embodiment, circuit substrate layer 615 comprises a low temperature plastic or thermoplastic resin such as polyethylene terephthalate (“PET”. In this embodiment, drive traces 620 and sense traces 625 may comprise printed silver ink. In another embodiment, circuit substrate layer 615 comprises a flexible circuit board, or fiberglass or glass and drive and sense traces (620 and 625) comprise Indium tin oxide (“ITO”) or copper. Layer 630, in one embodiment, comprises a layered combination consisting of adhesive-PET-adhesive, where the adhesive components are as described above with respect to layer 610. Layers 635, 640 and 645 comprise PET of varying thicknesses. As shown, the “bottom” surface of layer 640 has affixed thereon a second plurality of conductive drive traces 650 oriented in substantially the same orientation as first conductive drive traces 620. Raised and spatially offset support structures 655 and layer 660 also comprise a layered combination consisting of adhesive-PET-adhesive (similar to layer 630, see above). Layers 605-660 are affixed to and supported by base or stiffener plate 665. For example, in a portable or notebook computer system, base 665 could be formed from a rigid material such as a metal stamping that is part of the computer system's frame. Similarly, base 665 could be the internal framing within a personal digital assist and or mobile telephone. Table 1 identifies the thickness for each of layers 600-660 for one embodiment of touch pad 600.

TABLE 1 Dimensions for Illustrative Touch Pad 600 Layer Material Thickness (mm) 605 Polyester, polycarbonate film, glass or ceramic 0.3  610 Pressure sensitive adhesive (“PSA”) or 0.05  ultraviolet (“UV”) light cured adhesive 615 PET 0.075 ± 0.02 620 Silver ink, copper, Indium tin oxide 0.006 625 Silver ink, copper, Indium tin oxide 0.006 630 Layered PSA-PET-PET  0.03 ± 0.01 635 PET 0.075 ± 0.02 640 PET  0.1 ± 0.02 645 PET 0.125 ± 0.02 650 Silver ink, copper, Indium tin oxide 0.006 655 Layered: PSA 0.025 ± 0.01 PET  0.1 ± 0.02 PSA 0.025 ± 0.01 Active touch pad surface: 271 mm × 69 mm No of drive traces (620 and 650): 13 Number of sense traces (625): 54 Pixel seperation: 5 mm

In operation touch pad 600 measures the change (e.g., decrease) in capacitance due to cosmetic layer 605 being touched at one or more locations through the mutual capacitance between drive traces 620 and sense traces 625. In a manner as described above, touch pad 600 also measures forces applied to cosmetic layer as sense traces 625 and drive traces 650 are brought into closer proximity through the measured change (e.g., increase) in mutual capacitance between them. In this embodiment, raised structures 655 are used on both sides of the second layer of drive traces (650) to provide additional movement detection capability.

During measurement operations, each of drive traces 620 are stimulated in turn and, simultaneously, the change in mutual capacitance between drive traces 620 and sense traces 625 is measured. Once each of drive traces 620 have been stimulated (and the corresponding change in capacitance measured via sense traces 625), each of drive traces 650 are driven in turn and sense traces 625 are used to determine the change in mutual capacitance related to force (that is, the mutual capacitance change between traces 625 and 650 due to an applied force). In this manner, images of both the “touch” input and “force” input to cosmetic layer 605 can be obtained.

One of ordinary skill in the art will recognize that the above-described “scanning” sequence is not required. For example, drive traces 620 and 650 could be stimulated in overlapping fashion such that a first trace in drive traces 620 is stimulated, followed by a first trace in drive traces 650, followed by a second trace in drive traces 620 and so on. Alternatively, groups of traces in drive traces 620 could be stimulated first, followed by a group of traces in drive traces 650, and so on.

In one embodiment drive traces 620 (associated with touch location measurement operations) use a different geometry from drive traces 650 (associated with force measurement operations) and sense traces 625 (used during both location and force measurement operations). Referring to FIG. 7, it can be seen that drive traces 620 utilize conductive traces that employ internal floating plate structures 700 and, in addition, are physically larger than either the conductive traces used in sense 625 and drive traces 650 (both of which, in the illustrated embodiment, have the same physical size/structure). It has been found that this configuration provides increased sensitivity for determining where one or more objects (e.g., a finger of stylus) touch, or come into close proximity to, cosmetic surface 605.

Referring to FIG. 8A, in another embodiment of a combined touch and force sensitive touch pad in accordance with the invention (touch pad 800), raised structures 655 may be replaced by beads or polymer dots 805 (also referred to as rubber or elastomer dots). In this embodiment, beads 805 operate in a manner similar to that of raised structures 655 (see FIG. 6). As shown, beads 805 rest on a thin adhesive layer 810 and are sized to keep layers 630 and 640 at a specified distance when no applied force is present. One illustrative layout and spacing of beads 805 is shown in FIGS. 8B (lop view) and 8C (cross-section). Table 2 identifies the approximate dimensions for each component of touch pad 800 that is different from prior illustrated touch pad 600.

TABLE 2 Dimensions for Illustrative Touch Pad 800 Layer Material Thickness (mm) 805 Rubber or polymer (e.g., elastomer) 810 Pressure sensitive adhesive (“PSA”) or  0.015 ultraviolet (“UV”) light cured adhesive a Column bead separation 1.0 b Row bead separation 5.0 c Bead offset 2.5 ± 0.15 d Bead height  0.15 Active touch pad surface: 271 mm × 69 mm No of drive traces (620 and 650): 13 Number of sense traces (625): 54 Pixel separation: 5 mm

Referring to FIG. 9A, in yet another embodiment of a combined touch and force sensitive touch pad in accordance with the invention (touch pad 900), a single layer of deformable beads or elastomer dots 905 are used. In touch pad 900, thin adhesive layers 910 are used to mechanically couple the beads to the rest of the touch pad structure and the structure itself to base 665. One illustrative layout and spacing of deformable beads 905 is shown in FIGS. 9B (lop view) and 9C (cross-section). Table 3 identifies the approximate dimensions for each component of touch pad 900 that is different from prior illustrated touch pad 600.

TABLE 3 Dimensions for Illustrative Touch Pad 900 Layer Material Thickness (mm) 905 Rubber or polymer (e.g., elastomer) 910 Pressure sensitive adhesive (“PSA”) or 0.015 ultraviolet (“UV”) light cured adhesive a Column bead separation 1.0 b Row bead separation 1.0 c Bead offset 0.5 d Bead width 0.5 e Bead height 0.15 Active touch pad surface: 271 mm × 69 mm No of drive traces (620 and 650): 13 Number of sense traces (625): 54 Pixel separation: 5 mm

Referring to FIG. 10A, in another embodiment of a combined touch and force sensitive touch pad in accordance with the invention (touch pad 1000), spring membrane 1005 is used instead of raised structures (e.g. 530 and 655) or deformable beads (e.g., 805 and 905). In touch pad 1000, thin adhesive layers 1010 are used to mechanically couple PET spring 1005 to layers 635 and 640 as well as to mechanically couple layer 645 to base 665. Referring to FIG. 10B, in one embodiment spring membrane comprises a single rippled sheet of PET whose run-to-rise ratio (i.e., a/b) is typically in the range of approximately 10:1 to 50:1. One of ordinary skill in the art will recognize that the exact value used in any given embodiment may change due to a variety of factors such as, for example, the physical size of the touch pad surface, the amount of weight specified for full deflection (e.g., 200 grams) and the desired sense of “stiffness” presented to the user. Table 4 identifies the approximate dimensions for each component of touch pad 1000 that is different from prior illustrated touch pad 600.

TABLE 4 Dimensions for Illustrative Touch Pad 1000 Layer Material Thickness (mm) 1005 PET 0.75  1010 Pressure sensitive adhesive (“PSA”) or 0.025 ultraviolet (“UV”) light cured adhesive a/b Spring run-to-rise ratio 10:1 → 50:1 Active touch pad surface: 271 mm × 69 mm No of drive traces (620 and 650): 13 Number of sense traces (625): 54 Pixel separation: 5 mm

Referring to FIG. 11A, in another embodiment rippled spring membrane 1005 may be replaced by dimpled spring membrane 1105. In this implementation, spring membrane 1105 is a single sheet of deformable material (e.g., PET) that has dimples formed in it by, for example, thermal or vacuum forming techniques. FIGS. 11B and 11C show top views of two possible dimple arrangements. Two illustrative layouts (lop view) for dimpled membrane 1105 are shown in FIGS. 11B and 11C. As used in FIGS. 11A-11C, the “+” symbol represents a raised region and a “−” symbol represents a depressed region. Table 5 identifies the approximate dimensions “a” through “e” specified in FIG. 11A.

TABLE 5 Dimensions for Illustrative Spring Membrane 1100 Layer Material Thickness (mm) 1105 PET 0.075 a Dimple top length 1.0 b Dimple width 1.25 c Dimple separation 2.5 d Dimple rise and fall length 0.075

Various changes in the materials, components and circuit elements are possible without departing from the scope of the following claims. For example, drive traces and sense traces in accordance with FIGS. 1-10 have been described as being orthogonal. The manner in which drive traces and cut across or intersect with sense traces, however, generally depends on the coordinate system used. In a Cartesian coordinate system, for example, sense traces are orthogonal to the driving traces thereby forming nodes with distinct x and y coordinates. Alternatively, in a polar coordinate system, sense traces may be concentric circles while drive traces may be radially extending lines (or vice versa).

In addition, in the embodiments of FIGS. 1 and 2, drive layer 135 and drive traces 140 (and, therefore, connector 145) may be incorporated within and on spring membrane 125. That is, drive traces 140 could be laid down or etched on a surface of flexible membrane 125. Similarly, drive traces 535 could be incorporated into and as part of flexible membrane 525 (see FIG. 5).

One of ordinary skill in the art will also recognize that beads in accordance with FIGS. 8 and 9 (see FIGS. 8 and 9) could also be used in place of raised structures 130, 530 and 655 (see FIGS. 1, 2A, 2B, 5 and 6). Similarly, spring mechanisms 1005 (see FIG. 10) and 1105 (see FIG. 11) could be used in place of beads 805 (see FIG. 8), deformable beads 805 and 905 (see FIGS. 8 and 9) or raised structures 130, 530 and 655 (see FIGS. 1, 5 and 6).

Referring to FIG. 12A, in another embodiment force detection in accordance with the invention may be incorporated within a display unit rather than a touchpad. For example, system 1200 includes processor 1205, standard input-output (“I/O”) devices 1210 (e.g., keyboard, mouse, touch pad, joy stick and voice input) and display 1215 incorporating force detection capability in accordance with the invention. Referring to FIG. 12B, in this embodiment, display 1215 includes display element 1220, display element electronics 1225, force element 1230 and force electronics 1235. In this manner, user 1240 views display element 1220 of display 1200 through force element 1230. By way of example, display element 1220 and electronics 125 may comprise a conventional liquid crystal display (“LCD”) display. Force element 1230 may comprise a force-only sensor (e.g., similar to the embodiments of FIGS. 1 and 2) or a force and location sensor (e.g., similar to the embodiments of FIGS. 5-11). Force electronics 1235 may comprise processing circuitry as described in FIG. 4. That is, force electronics 1235 is capable of driving and sensing mutual capacitance signals as described in connection with a touch pad in accordance with the invention.

It will be recognized by those of ordinary skill in the art that use of the described force detection technology should, when applied to display 1215, utilize transparent or substantially transparent drive and sense traces such as that provided by ITO (i.e., rather than copper which is opaque). Similarly, the gap between the first layer of traces (e.g., drive traces) and a second layer of traces (e.g., sense traces) used to detect an applied force (see discussion above) should be transparent or substantially transparent. For example, compressible transparent spacers could be used to embody offset raised structures 130, support structures 655, deformable beads 805, 905 or spring membranes 1005, 1105. 

What is claimed:
 1. A location and force imaging system comprising: a first member that receives a force input on a first surface and that includes a first conductive element configured for receiving first drive signals for detecting a location of the force input; and a second member including a second conductive element configured for receiving second drive signals for detecting an intensity of the force input, the second member spatially separated from the first member through a mechanism by which the first and second members are brought into closer proximity when the force input is received by the first surface; wherein the first and second conductive elements are configured for generating information associated with an image of the intensity of the force input and an image of the location of the force input.
 2. The system of claim 1, wherein the first conductive element includes a first plurality of conductive traces.
 3. The system of claim 2, wherein the second conductive element includes a second plurality of conductive traces.
 4. The system of claim 1, further comprising a deformable member disposed between the first member and the second member, wherein the deformable member provides the mechanism by which the first and second members are brought into closer proximity when the force input is received by the first surface.
 5. The system of claim 4 wherein the deformable member includes a dielectric membrane.
 6. The system of claim 1, further comprising a plurality of sense traces for sensing the location of the force input and the intensity of the force input.
 7. The system of claim 1, further comprising a base layer adjacent to the second member.
 8. The system of claim 1, the mechanism comprising a deformable dielectric membrane disposed at least partially between and contacting at least a portion of the first and second members.
 9. The system of claim 1, further comprising a controller configured for receiving the information and computing the images of the intensity and location of the force input, and transmitting signals representing the images of the intensity and location of the force input.
 10. The system of claim 9, further comprising a host processor that receives the signals and performs command and control actions based on the images of the intensity and location of the force input.
 11. The system of claim 10, wherein the command and control actions include selecting an object displayed on a display unit. 